1. Field of the Invention
The present invention relates to a method of making low stress and low resistance rhodium (Rh) leads and, more particularly, to a method of making such leads by oblique ion beam sputtering followed by annealing.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, a slider that has write and read heads, a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic signal fields to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a nonmagnetic gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field into the pole pieces that fringes across the gap between the pole pieces at the ABS. The fringe field writes the aforementioned signal fields in tracks on moving media, such as in circular tracks on a rotating disk.
The read head includes a sensor that is located between nonmagnetic electrically insulative first and second read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In recent read heads a spin valve sensor is employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer, and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to an air bearing surface (ABS) of the head and the magnetic moment of the free layer is located parallel to the ABS but free to rotate in response to the aforementioned signal fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer. Rotation of the magnetic moment of the free layer relative to the pinned layer changes the resistance of the spin valve sensor. A sense current Is is conducted through the sensor so that the resistance changes cause potential changes in the aforementioned processing circuitry that are processed as playback signals. The spin valve sensor is characterized by a magnetoresistive (MR) coefficient dr/R, where dr is the change in resistance of the spin valve sensor and R is the resistance of the spin valve sensor before the change.
Because of high conductance (low resistance) and resistance to corrosion, gold (Au) is a desirable material for the aforementioned first and second leads that are connected to the read sensor. Pure gold (Au), when used as conductor leads, however, presents a problem due to nodule formation of the gold at the ABS. This is due to pressure and high temperatures within the head during operating conditions of the read head within a magnetic disk drive. The operating temperatures can vary between 80xc2x0 C. -120xc2x0 C. Pressure on the leads increases with an increase in temperature due to expansion of layers adjacent the leads such as the first and second read gap layers and the first and second shield layers which are adjacent the read gap layers. With pressure due to the aforementioned temperatures the gold (Au), which is soft, is squeezed out of the leads at the ABS of the read head causing the aforementioned nodules. The nodules can short the leads to the first and second shield layers or short across edge portions of sensitive elements of the read sensor causing a failure of the read head.
Because of the problems with gold (Au), leads have been made from tantalum (Ta) which does not have the nodule problem. Unfortunately, tantalum (Ta) has a significantly higher resistance than gold (Au) which results in increased noise of the read head unless the thickness of the tantalum (Ta) lead layers is increased. Unfortunately, an increase in thickness of the lead layers causes steps adjacent the read sensor which are replicated by subsequent layers all the way to the write gap which can cause the write gap of the write head to be curved. This is known in the art as write gap curvature and causes the write head to write curved magnetic impressions into tracks of a rotating magnetic disk which are then read by a sensor that reads straight across. This causes a reduction in the read signal which equates to less storage capacity of the magnetic disk drive.
Other nonmagnetic metals considered for leads are copper (Cu), tungsten (W), ruthenium (Ru), molybdenum (Mo) and rhodium (Rh). Copper (Cu) and tungsten (W) have a corrosion problem because of a necessary exposure of edge surfaces of all leads at the air bearing surface. Ruthenium (Ru) suffers from severe contamination due to particle generation during conventional sputter deposition. Conventional sputtering is any sputtering without an ion beam gun. Molybdenum (Mo) has a high corrosion at the ABS. Rhodium (Rh) does not suffer from the formation of nodules, corrosion at the air bearing surface or contamination, but has a relatively high stress and resistance during conventional sputtering in its as deposited state which is not improved with annealing. European Patent Application No. 93300239.6 with Publication No. 0552890A2 published Jul. 28, 1993 teaches that annealing rhodium(Rh) leads at 250xc2x0 C. for up to 7 hours does not reduce the as deposited resistance. This means that the microstructure of the rhodium (Rh) lead has not changed which indicates that the as deposited stress has not changed. It would be highly desirable if rhodium (Rh) could be employed for leads with lower stress and resistance. The lower resistance would enable the leads to be employed with less resistance generated noise and/or thinner leads so as to reduce write gap curvature. The high stress can cause the rhodium (Rh) lead layers to separate from the sensor causing an open circuit that destroys the read head.
A method is provided for forming low stress and resistance rhodium (Rh) conductor leads for a read sensor. In the present method a sputtering system has a sputtering chamber which has a target of the material to be sputtered, namely rhodium (Rh), a substrate supporting a wafer upon which the rhodium (Rh) leads are to be formed and an ion beam gun which directs an ion beam onto the target for sputtering rhodium (Rh) atoms from the target onto the wafer. The sputtering chamber typically has an outlet for drawing a vacuum and an inlet for inserting an inert gas, such as argon (Ar), into the chamber. In the present invention the surface planes of the target and the substrate are oriented at an angle with respect to one another which results in what is referred to hereinafter as oblique ion beam sputtering. The formation of the rhodium (Rh) leads by oblique ion beam sputtering is followed by annealing the leads at a high temperature for a predetermined period of time. In the fabrication of magnetic read and write heads the annealing can take place upon the annealing of photoresist layers to form insulation layers for the insulation stack of the write head.
An object of the present invention is to provide improved lead layers for a read sensor by forming them with oblique ion beam sputter deposition and annealing.
Another object is provide rhodium (Rh) lead layers for a read sensor which have reduced stress and resistance as compared to rhodium (Rh) lead layers formed by prior art methods.
A further object is to provide a method of making an electrical lead for a device which has reduced stress and lower resistance.
Still another object is to provide a method of making rhodium (Rh) leads for a read head which have reduced stress and lower resistance.
Other objects and advantages of the invention will become apparent upon reading the following description taken together with the accompanying drawings.